I would use percent time billable to clients on a weekly basis

Some agencies rely on billing records. If the employees are working on a project . The n their time spent on these related tasks are billed to it. Meanwhile, if they are not working on a specific project. then their time is billed internally. Good employees are those with high billable percentages compared with internal charges.

I recommend using efficiency frontier analysis based algorithms for performance evaluation. These algorithms are flexible and you can define your own evaluation conceptual model. For example, we did a performance evaluation research on an emergency departments' staff based on resilience engineering, job satisfaction and patients satisfaction concepts recently. for more information and better orientation you can check out one our latest publications entitled "Performance assessment and optimisation of a large information system by combined customer relationship management and resilience engineering: a mathematical programming approach". I hope you find this useful.